Curable resin compositions contain light- or heat-curable resins. In various industrial fields, curable resin compositions have been developed which have various physical properties required by the particular applications. One of the applications of curable resin compositions is sealing materials for use in boards on which electronic components, semiconductor chips, or other components are mounted. Electronic components, semiconductor chips, or other components are often mounted on boards by a surface-mount technology that allows for high density mounting, and in this case, electrically insulating sealing materials are used to seal them. As such sealing materials, curable resin compositions containing epoxy resins as main organic components are conventionally and widely used. However, when a cured product formed from such a resin composition is allowed to stand at a high temperature such as 200° C. or higher for a long period of time, the mechanical strength is reduced, resulting in the formation of cracks or separation from the object intended to be sealed. Therefore, improved heat resistance is needed.
Highly heat-resistant sealing materials that have been considered include curable resin compositions containing cyanate ester compounds with high glass transition temperatures. Curable resin compositions containing cyanate ester compounds that are disclosed include, for example, epoxy resin compositions essentially containing a trifunctional or tetrafunctional epoxy resin, a curing agent, a compound having at least two cyanate groups per molecule, and an inorganic filler (see Patent Literature 1); and thermosetting resin compositions obtained by incorporating an organoaluminum compound and an organosilicon compound containing, for example, a silanol group as curing catalysts into a thermosetting resin composition formed of a cyanate ester compound and/or its prepolymer alone or in combination with an epoxy resin (see Patent Literature 2).
Furthermore, examples of resin composition for sealing materials that are disclosed are resin compositions for liquid sealing materials which are formed from an epoxy compound and a polycarbodiimide resin with a proportion of the polycarbodiimide resin of 0.1 to 10 parts by weight per 100 parts by weight of the epoxy compound, and which is liquid or fluid at ordinary temperature (see Patent Literature 3); sheet-shaped sealing materials made of an organic resin mainly containing a polycarbodiimide (see Patent Literature 4); and filling materials for semiconductor sealing materials including an inorganic substance and an organic layer chemically bonded to the surface of the inorganic substance and containing a carbodiimide group as a functional group reactive with an epoxy resin (see Patent Literature 5).